Light beam rangefinder

ABSTRACT

A rangefinder comprises a projector furnishing a modulated light beam directed on to the object to be ranged and a receiver to pick up the reflected rays. The rangefinder is designed to avoid disturbances of the readings by chance interference signals. The receiver has a photoelectric cell at the front and rear of a mirror on to which some of the reflected rays are converged by a lens. The photocells are mounted for axial displacement so as to adjust for equal light reception according to the convergence and hence the range of the rays reflected from the object. The signals from the photocells are cut off and connected by a device actuated in rhythm to conform to a constant phase relationship with the light beam modulation. The cut off device connects the receiver to a storage device for the measured signals in which the stored sums of the interfering signals give a substantially nil value. The storage device is an RC element whose time constant is several times that of the beam modulation. The circuit includes a differential amplifier. Output signals from &#39;&#39;&#39;&#39;gate&#39;&#39;&#39;&#39; circuits control the axial displacements of the photocells by supplying a motor driving a threaded shaft bearing a tapped nut supporting the photocells. A camera incorporating the rangefinder has an objective adjustment ring coupled to respond to rotation of the shaft.

States atent Odone et al.

[ Mar. 28, 1972 [54] LIGHT BEAM RANGEFINDER Paillard S. A.,Sainte-Croix(Vaud), Switzerland [22] Filed: Sept. 15, 1969 [21]Appl.No.: 858,004

[73] Assignee:

CONTROL CIRCUIT CAMERA Primary Examiner-Richard A. Farley AssistantExaminer-S. C. Buczinski Attorney-Emory L. Groff and Emory L. Groff, Jr.

[57] ABSTRACT A rangefinder comprises a projector furnishing a modulatedlight beam directed on to the object to be ranged and a receiver to pickup the reflected rays. The rangefinder is designed to avoid disturbancesof the readings by chance interference signals. The receiver has aphotoelectric cell at the front and rear of a mirror on to which some ofthe reflected rays are converged by a lens. The photocells are mountedfor axial displacement so as to adjust for equal light receptionaccording to the convergence and hence the range of the rays reflectedfrom the object. The signals from the photocells are cutoff andconnected by a device actuated in rhythm to conform to a constant phaserelationship with the light beam modulation. The cut off device connectsthe receiver to a storage device for the measured signals in which thestored sums of the interfering signals give a substantially nil value.The storage device is an RC element whose time constant is several timesthat of the beam modulation. The circuit includes a differentialamplifier. Output signals from gate" circuits control the axialdisplacements of the photocells by supplying a motor driving a threadedshaft bearing a tapped nut supporting the photocells. A cameraincorporating the rangefinder has an objective adjustment ring coupledto respond to rotation of the shaft.

6 Claims, 5 Drawing Figures PAlENTfimrma x972 SHEET 1 OF 2 CONTROLCIRCUIT FOR MOTOR M1 INVENTOR S W/LLY 5 BY ATTORNEY PATENTEUMARZS We3,652,160

SHEET 2 BF 2 a; m as mu -rs D5 no ym C |--1 Lcu T11 POSITIVE 1 2AMPLIFIERS 2'71 THRESHOLD NEGATIVE TRIGGER PULSEIS g4 Mx GATE INVENTORSG a m/ww ODaNZ HE Mlle/c d KUN z M/L L/ B u c// ATTORNEY LIGHT BEAMRANGEFINDER The present invention relates to a light beam rangefinderand more especially to a rangefmder comprising a projection furnishing amodulated light beam directed on to the object whose distance is to bedetermined, a receiver intended to pick up the rays reflected by saidobject, these rays being exposed to disturbances arriving frominterference signals due to chance, this receiver comprising at leastone photoelectric element furnishing an electric signal in response toreflected light rays.

It is an object of the invention to render negligible the influence ofinterfering rays, in order to prevent the latter from falsifying theresults of the measurements. This object is achieved according to theinvention due to the fact that the rangefinder comprises a device forthe cutoff and connection of the signal furnished by the receiver, thisdevice being actuated in rhythm with the modulation of the light beam byhaving a constant phase relationship with respect to this modulation,this cutoff device connecting the receiver to a storage device for themeasured signals, in which the stored additions of the interferingsignal give an appreciably nil value.

In order that the invention may be more fully understood an embodimentof the invention is described below purely by way of illustrative butnon-limiting example, with reference to the accompanying schematicdrawing in which:

FIG. 1 shows very diagrammatically the general arrangement of oneembodiment of a light beam rangefinder according to the invention.

FIG. 2 shows an electrical circuit of the rangefinder of FIG. 1.

FIG. 3 shows a control circuit for the motor of the rangefinder, thiscircuit being controlled by a signal furnished by the circuit of FIG. 2.

FIG. 4 is a block diagram of a variation of one embodiment; 3

and

FIG. 5 shows the state of the electric signals at various points of thediagram according to FIG. 4.

The rangeflnder shown in FIG. 1 corresponds to the general principleindicated in the US. Pat. application Ser. No. 686,554 filed Nov. 29,1967 and which is now U.S. Pat. No. 3,558,894, granted Jan. 26, l97l.This rangefinder comprises a projector having an infrared ray lamp 1,placed at the focus of the reflector 2, so as to obtain a beam 3 withsubstantially parallel rays. This beam is directed on to an object 4whose distance it is desired to determine. The luminous spot, formed onthe object 4, reflects rays in the direction of a convergent receiversystem, constituted by two portions 5 and 6 of a bi-convex lens. Theseportions 5 and 6 are arranged on both sides of the reflector 2. The rays7, received by this converging system, converge behind the projector 2at a distance which varies as a function of the distance between therangefinder and the object 4.

The two convergent beams formed by the portions 5 and 6 are directedtowards the edges of a mirror 8, so that the rays passing above thisedge strike a photoelectric element 9, whilst the rays reaching themirror 8 are reflected by the latter towards a photoelectric element 10.Over a certain distance of convergence of the rays picked up by theportions 5 and 6, it is possible to balance the light fluxes strikingthe photoelectric elements 9 and 10.

If the object 4 recedes from the rangefinder, the distance ofconvergence of the rays formed by the receiver system becomes smaller,and a greater part of the light beams designated by 11 and 12 come tostrike the mirror 8 to be reflected towards the photoelectric element10. The quantity of light received by this element increases at theexpense of that received by the element 9.

If, on the other hand, the object 4 approaches the receiver system, thedistance of convergence of the rays detected increases and thephotoelectric element 9 receives additional light, whilst the light fluxstriking the element 10 diminishes.

By displacement of the elements 9 and 10 and of the mirror 8, it ispossible to measure the distance of convergence of the rays received andthrough this to determine the distance of the object on which therangefinder is directed. To this end, the mirror 8 and the elements 9and 10 are mounted on a support 13 which can be displaced by an electricmotor M driving a threaded rod 14 engaged in a nut 15 connected by afoot 16 to the support 13. To this purpose, the motor M is supplied by acontrol circuit 17 which is itself controlled by the photoelectricelements 9 and 10. The rangefinder is coupled to a camera 18 illustrateddiagrammatically and of which the objective 19 has a distance regulatingtoothed ring 20. The coupling is illustrated diagrammatically by anotched belt 21 driven by the motor M and transmitting the rotationreceived to a shaft 22 bearing a gear 23 engaged with correspondingteeth of the ring The control circuit 17 is shown in more detail inFIGS. 2 and 3. There, the photoelectric elements 9 and 10 are shown asbeing connected in series with a resistance R1 and R2 7 respectively,between the supply terminals a and b of a direct current source. As thebeam furnished by the lamp 1 is modulated at a relatively low frequency,for example comprising to form a Wheatstone bridge between 10 and Hz.,the light beams reflected and picked up by the receiver are alsomodulated, so that the drop voltage at the terminals of thephotoconductors 9 and 10 has an alternating component which is in phasewith the modulations of the beam. This alternating component of each ofthe photoconductors 9 and 10 is transmitted by a condenser C l and C2respectively, to a differential amplifier with two transistors T1 andT2.

As is well known per se, the two emitters of the transistors T1 and T2are connected to one terminal of the source of supply by a commonresistance R3, whilst the collectors are connected each to the otherterminal of this source by an individual resistance R4 and R5respectively. The bases of the 5 two transistors are biased by voltagedividers comprising two resistances R6 and R7, and R8 and R9respectively.

When the two photoconductors 9 and 10 are subjected to equal lightfluxes, they give rise to identical drops of alternating voltage, ofwhich the difference is nil, so that at the terminals of the resistanceR5 of the differential amplifier, no alternating component is found. Ifone or the other of the photoconductors receives a reflected beamgreater than the other, the alternating components transmitted by thecondensers C1 and C2 have a difference in amplitude, but of course, arealways in phase with the modulation frequency of the beam 3. In thiscase, an alternating voltage of the same frequency appears at theterminals of the resistance R5, this voltage being in phase, or incounter-phase with the modulation of the light beam according to whichof the two photoconductors 9, 10 is the most exposed to the reflectedrays.

The alternating current appearing at the terminals of the resistance R5is transmitted through a condenser C3 to the base of a transistor T3constituting an amplifier stage. The bias of the base of this transistorT3 is obtained by two resistances R10 and R11. The output voltage takenat the resistance R12 of the collector of the transistor T3 is appliedthrough a condenser C4 to a make-and-break device comprising twotransistors T4 and T5 whose collectors are connected to the twoterminals of a condenser C5.

The bases of the transistors T4 and T4 are connected to a multivibratorMX and controlled in counterphase so that when the transistor T4 isconductive, the transistor T5 is nonconductive and, when the transistorT5 is conductive, the transistor T4 is non-conductive inversely. Whenthe transistor T4 is conductive, the condenser C5 is connected inparallel with a resistance R13. When the transistor T5 is conductive,the transistor T4 being then nonconductive, the condenser C5 isconnected to the output of the amplifier comprising the transistor T3.

The multivibrator MX comprises two transistors T6 and T7, the base ofeach of these transistors being connected to the collector of the othertransistor by a condenser C6. and C7 respectively. The bias of the basesis obtained by the resistances R14 and R15, whilst the resistances ofthe collectors are designated by R16 and R17. The voltage at theterminals of the resistance R17 controls, through a resistance R18, thebase of a transistor T8 which is mounted in series with the lamp 1between the terminals of the supply source. In this way, the transistorT8 is alternately conductive and nonconductive, so that the lamp 1 issupplied by a current pulsed at the frequency of the multivibrator. Thelamp 1 thus supplies a luminous beam modulated in intensity.

The voltage at the terminals of the resistance R13 constitutes a pulsedelectrical signal of constant polarity which may be tapped at theterminal and d, and which indicated either the state of balance, or thatof the two photoconductors 9, 10 which receive the greatest modulatedflux.

It should be noted that the circuit described is insensitive tointerfering rays which can encounter the photoconductors 9 and 10. Infact, if the interfering ray is continuous, it does not give rise toalternating components in the voltage drop at the terminals of thephotoconductors, so that its effect is not transmitted to thedifferential amplifier. If the interfering light flux comprisesalternating components and is symmetrically distributed between thephotoconductors 9 and 10, the effects that it produces on thesephotoconductors is subtracted in the differential amplifier and does nottherefore appear at the output of the latter. If the interfering lightflux is not balanced between the two photoconductors 9, 10, it thengives rise to a voltage at the output of the differential amplifier.However, supposing that this interfering light flux is not furnished bythe lamp 1, it is possible that its frequency will be different from thefrequency of the modulation frequency of the said lamp. As thetransistors T4 and T5 are controlled according to a well determinedphase relationship with respect to the modulation of the lamp 1, thecondenser C5 constitutes a storage device which is successivelyconnected to the output of the receiver in rhythm with the modulation ofthe light beam. If the resistance R13 constitutes, with the condenserC5, and element RC of which the time constant is several times greaterthan the duration of the modulation period of the beam, the chargestored by the condenser C5 is only partially dissipated into theresistance R13 during the duration of closure of the transistor T4. Itfollows that the potential of the condenser C5 will rise in steps untilit reaches the average value for which, at each period of conduction ofthe transistor T4, its discharge into the resistance R13 is equal to thecharge that it receives when the transistor T5 is conductive.

Each charge of the condenser C5 comprises a part which depends on theillumination of the photoconductors 9 and 10 by the reflected modulatedlight beam and a part which arrives from an alternating interferinglight flux. As the first part is always measured for a phaserelationship determined with respect to the modulation of the lightbeam, these successive parts are added. On the other hand, theinterfering signals not being synchronized with the modulation of thebeam, their accumulated addition gives an average nil value. It therebyresults that the successive additions of the output signals enable thedetection of the interesting signal among the interfering signals whichcan have momentary values much greater than the interesting signal.

FIG. 3 shows a circuit enabling the driving of the motor M in onedirection or the other according to the relative exposure of thephotoconductors 9 and 10 to the reflected beam detected by the receiver.To this end, this circuit uses the electrical signal obtained at theterminals of the resistance R13 of the circuit according to FIG. 2. Thissignal is applied to the two terminals 0 and d which are connected tothe terminals 0 and d of FIG. 2.

The terminals c is associated with two diodes D1 and D2 constitutingrectifiers enabling the charging of one or other of the condensers C8and C9 as a function of the polarity and of the amplitude of the pulsesreceived at the terminals of the resistance R13. In fact, by reason ofthe existence of the differential amplifier in the circuit of FIG. 2, animbalance between the signals received by the photoconductors 9 and 10is manifested by positive or negative pulses, according to which ofthese two photoconductors is the most exposed to the reflected beam.Thus, if the terminal c' is subjected to positive pulses, the condenserC8 will transmit these pulses to the base of a transistor T8 biased bytwo resistances R19 and R20, the condenser C9 not receiving any changethrough the diode D2. On the contrary, if the pulses are negative, it isthe condenser C9 which transmits these pulses to the base of atransistor T9, whilst the diode D1 blocks any signal in the direction ofthe transistor T8.

Thus, the positive pulses are amplified by the transistor T8, whilst thenegative pulses are so by the transistor T9. The collectors of these twotransistors are connected each to a rectifier element D3, R21, C10 orD4, R22, C11, respectively, so that the positive and negative pulsesrespectively, make a continuous voltage appear at the base of the twotransistors T10 and T11 which each controls the supply of the motor M.When the transistor T10 is conductive, the current arising from thepositive terminal a passes through a resistance R23 to traverse themotor M, the transistor T10, and return to the terminal d which isconnected to the negative pole of the supply source. If on the contrary,it is the transistor T1 1 which is conductive, the current arising fromthe terminal a traverses a resistance R24, then the motor M in reversedirection from the preceding case, to return to the terminal d throughthe conductive transistor T1 1.

One can, of course, depart from the scheme described above and achievethe same object by other means. Thus, the storage device constituted bythe element RC comprising the condenser C5 and the resistance R13 couldbe replaced by a condenser connected so as to receive a succession ofelemental charges each corresponding to the measurement effected in thecourse of a period of the modulation of the light flux, this condenserbeing discharged after it has stored several elemental charges. Theaverage value of the signal detected could then be deduced either fromthe time of charge necessary to obtain a certain potential at theterminals of the condenser, or from the discharge current of thecondenser after certain interval of time. The successive measurementscould also be added in a digital electronic adding device.

FIG. 4 illustrates schematically a variation of execution tending toachieve maximum safety and insensitivity of the rangefinder tointerferences of short duration, but extremely violent. This embodimentassumes that the rangefinder comprises a circuit according to that ofFIG. 2, which gives, between the terminals c and d, a signalcorresponding to the curve g of FIG. 5, that is to say a succession ofpositive pulses having a certain phase relationship with respect to thecurve f showing the modulation of the light beam. In addition, therangefinder must comprise means to form a signal conforming to curve hof FIG. 5, this signal being formed by negative pulses having anotherphase relationship than the signal g with the modulation f of the lightbeam.

The means for obtaining the signal h can consist of a simple repetitionof the condenser C5, of the resistance R13, of transistors T4 and T5 ofFIG. 2, the control voltages of the transistors T4 and T5 being crossedin this case.

The diagram according to FIG. 4 comprises two amplifiers 24, 25 of whichthe input signals are represented by the curves g and h of FIG. 5. Theoutputs of these amplifiers 24 and 25 are coupled, so that the resultingsignal at their output is given by the curve 1' which is the sum ofcurves g and h. This signal comprises a succession of positive andnegative pulses which are applied at the input of an input thresholdtrigger 26. This trigger can be constituted by a bi-stable balance whoserocking movements in one direction are controlled by a positive pulseexceeding a predetermined threshold value, the rocking in the otherdirection being produced by a negative input pulse also exceeding apredetermined level. Thus, the application of the signal i of FIG. 5 atthe input of the trigger 26 enables an output signal to be obtained fromthis latter corresponding to the curve i of FIG. 5. This latter signalis applied to a difierentiator 27 to be transformed into a signal givenby the curve k of FIG. 5, this signal consisting of a series ofalternated positive and negative pulses.

The signal k is applied to the input of two circuits gate 28 and 29which are controlled by the multivibrator MX, so as to open and closedat the same time. The circuit 28 is intended to allow positive pulses topass, whilst the circuit 29 can allow to pass the negative pulses. Ifthe positive pulses of the signal k arrive at the circuit 28 during themoments of opening of the latter, an output signal from the gate circuit28 is obtained, which signal is used to control the rotation of themotor M (FIG. l) in a predetermined direction. The rotation of thismotor in the direction is controlled by the output signal of the gatecircuit 29 which is obtained when it is negative pulses that are appliedat the input during the opening of circuits 28 and 29.

if a very strong interference comes to modify the signal according tothe curve i of FIG. 5 so that it causes the complete disappearance of apositive or negative pulse, or even its replacement by a pulse ofreverse polarity, the absence of the pulse in question would suppress arocking movement of the trigger 26. The latter would thus remain in itsposition until the re-establishment of alternate pulses of the curve i.The momentary blockage of the trigger 26 results in the suppression ofpulses of the curve k and hence of any output signal beyond the gate"circuits 28 and 29. Thus, the appearance of an abrupt and intenseinterference signal cannot introduce an error into the control signal ofthe motor M, but causes the suppression of this signal until the end ofthe interference. The motor M hence remains in its existing positionuntil the operation conditions are re-established as normal.

it will be understood that various changes and modifications may be madein the embodiments described without departing from the essentialconcept of the invention as defined in scope by the appended claims.

1. A rangefinder comprising a projector furnishing a modulated lightbeam directed on to the object whose distance is to be determined, areceiver adapted to pick up the rays of said modulated light beamreflected by the object, said rays being subject to disturbances arisingfrom chance interference signals, said receiver comprising at least onephotoelectric element furnishing an electrical signal in response to thereflected light rays, said rangefinder comprising a make-andbreak devicefor cutting off and connecting the signal furnished by the receiver,said device being actuated in rhythm with the modulation of the lightbeam by having a constant phase relationship with respect to saidmodulation, said make-and-break device connecting the receiver to astorage device for the measured signals and for the interference signalsas well, in which the stored sums of the interference signals give anappreciably nil value.

2. A rangefinder according to claim 1, wherein said storage device isconstituted by an RC element whose time constant is several timesgreater than the duration of a period of the modulation of the beam.

3. A rangefinder according to claim 2, comprising two photoconductorsconnected respectively to two inputs of a differential amplifier, oneoutput of which is connected to a terminal of a condenser of which theother terminal is con nected to a resistance to form said RC element,the two terminals of the condenser being connected to earth by twoelectronic interruptors controlled so as to be alternately conductive.

4. A rangefinder according to claim 2, comprising at least onedifferential amplifier of which the two inputs are connected to twophotoconductors furnishing two signals of opposite signs, said twophotoconductors being displaceable to enable the determination of thepoint of convergence of the reflected rays picked up by the receiver,said differential amplifier comprising two make-and-break devicesactuated in phase opposition with respect to one another, each deviceacting on one of the said signals so as to furnish pulses of onepolarity for one of the signals and of the other polarity for the othersignal, said pulses of each polarity being applied to the input of atrigger at an input threshold, the output of said trigger is applied toa differentiator, the pulses of alternate polarities furnished by saiddifiereptiator being applied to two gate circuits controlledrespectively in phase and counterphase with the modulation of the lightbeam, the output signals of one of said gate circuit and of the othercontrolling the displacements of the photoconductors in one directionand the other direction respectively.

5. A rangefinder according to claim 4, including displacement means forsaid photoconductors comprising an electric motor driving a threadedshaft, a tapped nut riding on said shaft and supporting thephotoconductors.

6. A rangefinder comprising a projector furnishing a modulated lightbeam directed on the object whose distance is to be determined, areceiver adapted to pick up the rays of said modulated light beamreflected by the object, said rays being subject to disturbances arisingfrom chance interference signals, said receiver comprising twophotoconductors furnishing electrical signals in response to thereflected light rays, said two photoconductors being each connected totwo resistances to form therewith a bridge, a differential amplifierhaving two input transistors, two condensers each connected to one ofsaid two input transistors to apply thereto the output signal of saidbridge, said rangefinder comprising a make-andbreak device for cuttingoff and connecting the signal furnished by the receiver, said devicebeing actuated in rhythm with the modulation of the light beam by havinga constant phase relationship with respect to said modulation. saidmake-and-break device connecting the receiver to a storage device forthe measured signals and for the interference signals as well, in whichthe stored sums of the interference signals give an appreciably nilvalue.

1. A rangefinder comprising a projector furnishing a modulated lightbeam directed on to the object whose distance is to be determined, areceiver adapted to pick up the rays of said modulated light beamreflected by the object, said rays being subject to disturbances arisingfrom chance interference signals, said receiver comprising at least onephotoelectric element furnishing an electrical signal in response to thereflected light rays, said rangefinder comprising a make-and-breakdevice for cutting off and connecting the signal furnished by thereceiver, said device being actuated in rhythm with the modulation ofthe light beam by having a constant phase relationship with respect tosaid modulation, said make-and-break device connecting the receiver to astorage device for the measured signals and for the interference signalsas well, in which the stored sums of the interference signals give anappreciably nil value.
 2. A rangefinder according to claim 1, whereinsaid storage device is constituted by an RC element whose time constantis several times greater than the duration of a period of the modulationof the beam.
 3. A rangefinder according to claim 2, comprising twophotoconductors connected respectively to two inputs of a differentialamplifier, one output of which is connected to a terminal of a condenserof which the other terminal is connected to a resistance to form said RCelement, the two terminals of the condenser being connected to earth bytwo electronic interruptors controlled so as to be alternatelyconductive.
 4. A rangefinder according to claim 2, comprising at leastone differential amplifier of which the two inputs are connected to twophotoconductors furnishing two signals of opposite signs, said twophotoconductors being displaceable to enable the determination of thepoint of convergence of the reflected rays picked up by the receiver,said differential amplifier comprising two make-and-break devicesactuated in phase opposition with respect to one another, each deviceacting on one of the said signals so as to furnish pulses of onepolarity for one of the signals and of the other polarity for the othersignal, said pulses of each polarity being applied to the input of atrigger at an input threshold, the output of said trigger is applied toa differentiator, the pulses of alternate polarities furnished by saiddifferentiator being applied to two ''''gate'''' circuits controlledrespectively in phase and counter-phAse with the modulation of the lightbeam, the output signals of one of said gate circuit and of the othercontrolling the displacements of the photoconductors in one directionand the other direction respectively.
 5. A rangefinder according toclaim 4, including displacement means for said photoconductorscomprising an electric motor driving a threaded shaft, a tapped nutriding on said shaft and supporting the photoconductors.
 6. Arangefinder comprising a projector furnishing a modulated light beamdirected on the object whose distance is to be determined, a receiveradapted to pick up the rays of said modulated light beam reflected bythe object, said rays being subject to disturbances arising from chanceinterference signals, said receiver comprising two photoconductorsfurnishing electrical signals in response to the reflected light rays,said two photoconductors being each connected to two resistances to formtherewith a bridge, a differential amplifier having two inputtransistors, two condensers each connected to one of said two inputtransistors to apply thereto the output signal of said bridge, saidrangefinder comprising a make-and-break device for cutting off andconnecting the signal furnished by the receiver, said device beingactuated in rhythm with the modulation of the light beam by having aconstant phase relationship with respect to said modulation, saidmake-and-break device connecting the receiver to a storage device forthe measured signals and for the interference signals as well, in whichthe stored sums of the interference signals give an appreciably nilvalue.